4.1.0

• Bugfix: when passing an integer as an id to a listener, convert it to string so that it can be then passed as part of x.from without triggering an error.
• Bugfix: if passing a falsy value for an id field (either 0 or an empty string), use it instead of generating a random id.
• All functions now use r.error (which defaults to teishi.clog) to handle errors.
• r.prod can now be set to true to enable production mode (validations are skipped).
• Listeners of equal priority are now run by oldest first, to avoid execution sequences of unspecified order. The index property (an integer) was added to listeners for this purpose, plus the variable r.count to keep the count of how many listeners were added already.
• Allow for disabled flag in listener to turn it off temporarily (without having to forget it).
• Add benchmarking at the end of the test suite.
• Internal change: remove unnecessary argument iteration in r.mill.